Control surfaces are used on aircraft to influence the passage of fluid over various flight surfaces such as wings. Flaps, for example, are a type of control surface which are mounted to the rear of a wing and can be rotated with respect to the wing trailing edge to change the shape of the aerofoil profile of the wing assembly as a whole. This helps prevent wing stall at low speeds (e.g. during landing) when the flaps are fully deployed, and increases efficiency of the wing at high speeds (e.g. during cruise) when the flaps are stowed. Slats are another type of control surface positioned at the leading edge of the wing.
Both immovable and movable components (e.g. control surfaces such as flaps) need to be securely mounted to the aircraft. Flaps, for example, can be mounted to the wings of the aircraft in a variety of ways, for example via an underslung beam attached to the underside of the aircraft wing, or via a cantilever rib mounted directly to, and projecting perpendicularly from, a rear spar of the wing.
Cantilever ribs are attached to the rear spar of an aircraft wing and are generally bolted directly to the wing skin overhanging the spar and to the spar itself. The wing skin overhanging at both the upper and lower surfaces of the wing trailing edge and the upper and lower skin surfaces tends to converge. As such the vertical distance between the upper and lower skin at the trailing edges is somewhat less than the distance between the skins proximate the spar, i.e. the position at which the rib needs to be attached. Consequently, the rib cannot fit between the skins without them being spread.
As cantilever ribs are prone to damage (due to their exposed position on the aircraft), they need to be replaced frequently. On metal skinned aircraft this has been achieved by spreading the skins to increase the distance between their trailing edges.
Metal components can be repeatedly deformed in this manner as they generally have a high yield strength and will return to their original shape once released.
Composite (e.g. carbon reinforced plastic) components, which are now starting to be used for aircraft wing structures are more prone to damage following significant and/or repeated deformation such as spreading. As such, replacement of cantilever ribs in aircraft wings of this type is problematic.
It is an aim of the invention to provide an improved aircraft structure.